Magnetic core construction



July 15, 1952' F. R. DENTREMONT MAGNETIC CORE cousmucuou 2 SHEETS-SHEET 1 Filed Nov. 10, 1949 Inventor": Frank in RDEnbremonb,

y His Abnrne y 15, 1952 F. R. D'ENTREMONT 2,603,691

MAGNETIC CORE CONSTRUCTION Filed NOV. 10. 1949 2 Sl-TEETSSHEET 2 Inventor: Franklin RDEnbremont,

b WWI wk His Attorney,

Patented July 15, 1952 MAGNETIC CORE CONSTRUCTION Franklinlt. DEntremont, v.L'yunfield, ,iMass assignor to General ElectricConip'any, a corporation of New York Application November 10, 1949, Serial No. 126,571

. 11 This invention relates. to stationary electrical inductionapparatus, and more'particularly to .an improved magnetic v core construction for such apparatus.

In the construction of magnetic cores for'stati'onary'. electrical induction apparatus,- one of the probiems-which is encountered is that of the magnetic'saturation-and'core losses which occur due to' 'theejointszin. the laminated'material which constitutes the magnetic core. An illustration. of this problem can be found in th'e case of .magnetic' cores' formed of rolled striplrnagnetic material such as silicon strip steel. It lisic'onventionaltto formv suchcores of a pluralityot fstrips of thef desired magnetic material which are bent to give the': required: core configuration Such'acore is generally in theform of a' closed loop having a7 hollow'center; with the respective ends of each i of the constituent laminated strips being jointed in order I to form the noses-100p; Unless'theen'ds of the i respective magnetic strip's' forming' the core are' perfectly bi'itt jointed, which is unlikely, it can be demon s'ti ated that thefluxdensity in the joint section of 'th'e core willbe f considerably higher than in other sections of the core since the joints in men decrease the cross-sectional area of the core wherever they occur. Thisincrea'sed'flux density is", of course, undesirable since it causes increased core losses and other undesirable effects:

The-ideal condition' would be to have no joints in the magnetic circuit atall', and the next" best condition would-be to have thejoints co'mpletely staggered and distributed around the magnetic cli ciiitw As neitherof' the aforementioned conditions can-be obtained with a reasonable manufacturingoost, anyconstruction that will approach the results that could be obtained-under the ideal conditions should be' of considerable value:

Accordingly, it is anobject' ofthis invention to provide am new and improved joint"- construction for magnetic'cores.=.

It iis' a furthei' obj ect of this 'inve'ntion toprovi'd'e a joint. construction for magnetic cores whim-mu: provide improved magnetic and inechanical characteristics.

It is 'a" still further object of this invention to provide a ma'gneti'c core-inwhich the jointsof thei'laminations comprising the "core are so distributed. to give improved" magnetic characteristics.

Imaccordancei with these objectives, this inventionprovides' a joint construction for a magsiclaims. (01.175 -356)" netic core in which a plurality of groups of joins areused, the various groups of joints being displaced from one another either transversely or longitudinally of the core, with the respective joints within each joint group being staggered with respect to one another in accordance with the same or a similar predetermined pattern. I

The features of this invention which I believe to, be. novel are set forth-with particularity-in the appended claims. My inventionitself, however, both as to its organization and use, together with further objects and advantages thereof, may

' best be understood by reference to the following a differentinumber of layers per group-.-.

descriptiontaken in connection with the accompanyingtdrawingsin which Fig; 1 represents a view-in perspective of a magnetic core formed of magnetic strip material, having joints in accordance with my invention; and in which Fig. 2 representsza magnetic core constructed of flat punchi-ngs and having a joint arrangement in accordance with myinvention;

Referring now to Fig. 1, there is shown a laminatedmagnetic core I, which is formed of a plurality of strips 2 of some suitable rolled magnetic material; such as silicon steel; Knowing the in ner and; outer peripheral distances of the=core and-the-thickness of the-core, the-strips Z-may be precut'into ,the lengths necessaryto form the joint pattern to'be described hereinafter. They may be cuteither by hand oron a suitableindex shearingmachine; These precut strips may then be assembled and: expanded intoa desired coreconfiguration in accordancewith any. suitable -methods such as, for example, those de scribed in Patent 2,456,457-Sommervi1le, which is assigned tothe same assignee as the present application.

Inaccordancewith my invention, I have ,divided the laminated layers of themagnetic core I into :a plurality of groups for jointingpurposes. In the embodiment illustrated in the drawing, I have used: four. laminatedlayer groups, with each group-being composed-of four consecutive laminations. However, .it will beunderstood that I mayuse a'd-ifferent number of layer'groups with Thus, layer groupI iscomprised of layers numbered3, 4, 5'; and 6; group'II is comprised of layers 1, 8,n9',-' and I0; group III is comprised of layers ll, [2, l3, and Mzand group IV is com prised of layers-l5, l6; l1;andl8.-

Ari'inspectionof the joint pattern in the core shown in the drawing'reveals that each complete oblong lamination layer is comprised of an 2 upper inverted U shapedi lamination, andalower U-shaped lamination, with the respective leg members for each layer meeting in a joint on both the left-hand and right-hand core legs. That is, each laminar layer is jointed in two places, one joint being in the left-hand core leg, as viewed in the drawing, and the other joint being in the right-hand core leg.

In order to obtain a joint pattern in accordance with my invention, I provide alternate groups of long and short upper inverted U-shaped laminations, with corresponding short and long lower U-shaped laminations. That is, thelaminar layers 3, 4, 5 and 6 of the group and layers ll, I2, [3, and M of group III are formed by joining long upper inverted U-shaped strip members to short lower U-shaped strip members. Similarly, the layers 1, 8, 9, and ll] of group II and l5, l6. l1, and I8 of group IV are formed by joining short upper inverted U-shaped strips to long lower U- shaped strips. Thus, I have built up the core by alternately stacking groups of long, and short upper laminations, with the corresponding groups of lower laminations being short and long.

Due to lengths of the upper and lower members of the various laminated layers, as justdescribed, the joints in layer groups II and IV are locatedin the upper end of the core, as viewed in the drawing, while the joints in layer groups I and III are located in the lower part of the core. While the joints of both layer groups II and IV are located in the upper end of the core, yet these two groups of joints are offset from each other transversely of the core due to the intervening layers of group III. Likewise, the joints for layer groups I and III in the lower part of the core are offset from each other transversely of the core due to the intervening layers of group II.

Furthermore, in accordance with my invention, the joints within each group ar staggered with respect to one another so that adjacent layer joints within a given group are displaced from one another lengthwise of the core a relatively much greater amount than the joint displacement of alternate layers. It will be seen that the laminations within each group differ in length from one another, with an appreciably greater length differential between adjacent laminations than between alternate laminations.

Thus, considering, for example, the lamination layers of group I in the left-hand core leg, it will be seen that while the laminated layers -3,-4, 5, and 6 of group I are as a group all comprised of upper inverted U-shaped members having long left 'legs and lower U-shaped members having short left legs, yet the legs of the upper members for layers 3 and 5 are considerably longer than the corresponding legs for the upper members of layers 4 and 6.

- Conversely, in the right-hand core leg, the legs of the upper U-shaped members composing layers 3 and *5 are shorter than the corresponding legs of the upper members for layers 4 and 6.

In order to improve the mechanical strength and characteristics of the core, the left-hand and right-hand legs of each of the inverted upper U-shaped members and lower U-shaped members are made of unequal length in the manner 'just described for the layers of group I. While both legs of each U-shaped member are always in the same length category, 1. e., long or' short, yet there is always a differential in length be tween the legs for the rightand left-hand leg members.

In accordance with my invention, the lengths 4 of the upper and lower U-shaped laminar strips are arranged so that the lower and upper joints, respectively, of joint groups in the same region of the core are progressively stepped in the same direction in such manner as to lie along the same oblique line transverse of the core. Thus, for example, joints for layers 3 and 5 of group I and joints for layers H and 13 of group III are progressively stepped downwardly these four joints defining an oblique line DD which is directed slightly downwardly toward the outer edge of the core. Similarly, joints for layers 4, 6, l2, and I4 of groups I and III define an oblique line C-C which is parallel to, but higher than, the line D-'D defined by joints for layers 3, 5, I l, and [3. At the upper end of th core leg, joints for layers 8, l0, I6, and I8 of joint groups II and IV, are progressively stepped upwardly to define an oblique line BB which is directed upwardly toward the outer edge of the core leg. Also, joints for layers 7, 9, l5, and ll of joint groups R and IV are progressively stepped upwardly to define an oblique line AA which is parallel, but above, the line BB defined by the joints for layers 3, Ill, l6, and l8.

The effect of the length difierentialbetween the opposite legs of each of the U-sha'ped laminar members as previously mentionedis best shown by the juxtaposition inv the relation between lines A-A, A'A' and BB, B'B and between C-C, CC' and D--D, DD, which are defined by the joint patterns on the two core legs. Thus, while lines A-A and A,-A" are defined by joints for layers 1, 9, l5, and H- in the lefthand and right-hand core legs respectively, and

lines B-B and B'-B are defined by joints for layers 8, l8, l6, and I8 in the left-hand and righthand. core legs, respectively, it will be noted that line A-A is higher than line B-B in the lefthand core leg but that line AA' is lower than line BB in the right-hand core leg. Similarly, line C-C, defined by joints for layers 4, 6, l2, and I4 is higher than line DD, defined by joints for layers 3, 5, II, and I3 in the left-hand core leg, but line CC is lower than line DD' in the right-hand. core leg.

There is shown in Fig. 2 an embodiment of my invention as applied to a magnetic core constructed of fiat punchings. The magnetic core shown in Fig. 2 is constructed of a plurality of layers of fiat punched U-shaped laminations assembled to form a magnetic core of generally hollow rectangular shape. Each laminated layer comprises two U-shaped punchings having their respective leg members placed end to end in a butt joint to form a closed loop. Each laminated layer has one U-shaped punching with short legs which mates with a U-shaped punching having long legs.

In accordance With'my invention I stack alternate groups of longand short-legged U-shaped punchings at a given end of the magnetic core so that adjacent groups of laminated layers have their respective joints at opposite ends of the core. Furthermore, within each group of laminated layers I have staggered the joint arrangement so that joints within a given group are offset from one another. j

Referring now to Fig. 2, it will be seen that the four topmost layers I9, 20, 2|, and 22 have long U-shaped punchings with legs which extend well into the lower part of the core legs. Thus, the joints for layers [9, 20, 2|, and 22 are 'all in the lower part of the core with respect to the view shown in the drawing. However, the secof thecore leg;

ageosgeoi and group of I laminated layers including: layers 235*, 2'5, :and' 26 "have the respective -legs":otithe upper and lower U sh'aped punchings of:- such length that the joints between the: uppers: and lower r punchings: are :the uppenportion-of the core with respect to the-view shown in the draweingr The third' group oflayers incl-uding layers 21, 28; 29-;Land 30 are 'positined in the lower part ofthe core'and the rourtn. group ofilayersincludtnglayers 31; 32, 33, and '34 have their joints positionedihthc upper portion .of F the aorewith respect to' the viewshownsin the drawing; Thus, it" will be seen that in accordance with =m-y-invention I1position'the: j oints f or a group 01 adjacent laminar layers at -oneendtof'ithezcorw'leg with the a'd-jacent group of? laminar layers being jointed atthe: opposite end'of thesame core leg; Furthermore;- I' stagger the joints within each group-s0 that the joints: within a g-iveirgroup are offset from oneanother; although all jo'ints in -a: given group are-in tlie==same general region Thus; the joints" in layers 19; 21," and 22, while all in:thelriwerregionof the" core -leg, withv respect. to the view= Show-n in the drawing, are ofiset from one-anotlrierinv such manner as to define two lines C-'-C and D'D extending transversely and 1 obliquelyacross the coreuleg; Similarly, the joints for layers 21'; 2'8, 28'; and :3'0g which are also in the lower-- region of the core, ares tag-gered' from oneanother and I prefer to so position these joint's as-to lie along the 1 same lines :1 C"C and =DiDI" In the upp part- .of-fthewcore, with-respect to the viewshown in the. drawing,- the joints for'layerss23, 24;

and 2fi are-ofisetirom one another in such manher as to define the lines EE and FF extending transversely and obliquely across the core leg, and similarly the joints:v f or layers 3 I, 32,

33, and 34 are offset from onezanother; and-:1 prefer to so position these jointsthatthey also lie along the lines E-E and F-F.

In the opposite core leg, U-shaped punchings are+in the same leng-th'category as in the *leg 'just described. Thatis; U-shapedipunchingswhich arezshortin one legarealso' sh'ort inthe-other coreleg. However, I preferto reverse-the-ofiset relation within each I group of adj acentlaminations. in such manner that th-e-joints whichare on line C"-'-C in theleft-core legwill fall along line CC' in the right core leg, and the joints for layers which are jointed along line D-D in the left core leg will be jointed along line D'--D' in the right core leg. Similarly, joints for layers which are jointed along line EE in the left core leg are preferably jointed along E'E' in the right core leg, and layers which are jointed along line F-F in the left core leg are preferably jointed along the line F-F' in the right core leg.

It can be seen that I have provided a plurality of groups of joints for the laminations comprising the core of a stationary electrical induction apparatus, with each of the groups being displaced from the others either transversely or longitudinally of the core, and with the component laminations making up each of the groups having their joints staggered or stepped with relation to each other. By this means, I maintain practically uniform flux density throughout the core despite the joints, in contrast to the greatly increased flux density which would be experienced if all of the joints were concentrated in the same core cross-sectional area.

While I have shown in my drawing and description a core having only four joint groups,

with each; grouphaving four 1aminati'ons,- itd's obvious 1 that 1 a greater number of 'groups 4 could be::used; and that. a: greater number of laminattions could: be used in each lgroup, ,reitherin creasingthe: number of: steps :or the =number of laminations 'per step: I It also: obvious that wherever Iliave shown or described a single layer of laminated magnetic" material, such a: single layer may: represent: a plurality" of laminated layersa While 1 there have:- been shown: and? described particular embodiments of I my invention; it will be obvious thoseskilled in the: art'; that vari ous= changes andmodifications1 can be: made therein: without: departing? from the invention, and; therefore, it is* aimed: in theappended claims: to cover all ':such changes and: modifications :as fall within 1 the ture' spirit and 1 scope- 0f the invention.

What I claim as new 'and -desire to secure by Letters-Patent of the United States is:

l. A -magnetic core for stationary electrical induction apparatus" comprising a plurality of layers of magnetic: material, said plurality of layers-- of magnetic material comprising" a plurality of superposed layer groups of laminated magnetic material each of-said layers forming a-c-losed 'loop having a hollowcenter; each of saidlayersbeing formed of 'two U -shaped mag netic members-having their respective leg members joinedend-to-end inabutt "joint to form said closed loop, the joined -leg members of said U -shapedmembers constituting the legs of said magneticcore, the joints for-said plurality of layers being disposed in a plurality of groups along-= the respective legs of said magnetic core to reduce magnetic saturationin th'ejoihtareas, each layer group in agiven core leg'- having a joint 1 group: corresponding I thereto; joint groups for-adjacent groups of'laminated layers lying in a'g-iven coreleg beingpositioned at opposite ends of that core leg; joint groups for alternate groups of laminated layerslyingina givencore legbeingpositioned at the sameend of that core leg;- and-asta gered arrangement within each joint groupso thatf joints foreven-nurnbered layerswithin-each la-yer "groupare progressively o-ii'set' in thesame' direction and define a line running obliquely'of the thicknessof saidlayers of magnetic material, the joints for odd-numbered layers within each layer group being progressively offset in the same direction as the joints of said even-numbered layers, and also defining a line running obliquely of the thickness of said layers, the respective lines defined by the joints of said evenand odd-numbered layers of each joint group being substantially parallel to each other but displaced from each other by a substantially greater distance than the distance separating adjacent joints lying on a given oblique line, the two oblique lines defined by each joint group at an end of a given core leg being substantially co-linear with the two oblique lines defined by the other joint groups at said end of said core leg.

2. A magnetic core for stationary electrical induction apparatus comprising a plurality of layers of magnetic material, said plurality of layers of magnetic material comprising a plurality of alternate groups of long U-shaped laminations in superposed relation with alternate groups of short U-shaped laminations so that adjacent groups of said laminations are of opposite length, each of said layers forming a closed loop having a hollow center, each of said layers being formed of two U-shaped magnetic laminations having their respective leg members joined end-to-end in a butt joint to form said closed loop, the joined leg members of said U- shaped' laminations constituting the legs of said magnetic core, said core being formed by stacking alternate groups of long and short U-shaped laminations mating with corresponding groups of short and long U-shaped laminations, to thereby cause joints for adjacent groups of laminations lying ina given core leg to be positioned at opposite ends of that core leg and joints for alternate groups of laminations lying in a given core leg to be positioned atthe same end of that core leg, and a staggered arrangement within each group so that joints for even-numbered layers within each group are progressively offset in the same direction and define a line running obliquely of the thickness of said layers, the joints for odd-numbered layers within each group being progressively offset in the same direction as the joints of said even-numbered layers, and also defining a line running obliquely of the thickness of said layers, the respective lines defined by the joints of the evenand odd-numbered layers within a given group being substan tially parallel to each other but displaced from each other by a substantially greater distance than the distance separating any two adjacent joints lying on a given oblique line within that group, the two oblique lines defined by each group at an end of a given core leg being substantially co-linear with the two oblique lines defined by the joints of the other groups at said end of said core leg.

3. A magnetic core for stationary electrical induction apparatus comprising a plurality of layers of magnetic material, said plurality of layers of magnetic material comprising a plurality of alternate groups of long U-shaped laminations in superposed relation with alternate groups of short U-shaped laminations so that adjacent groups of said laminations are of opposite length, each of said layers forming a closed loop having a hollow center, each of said layers being formed of two U-shaped magnetic laminations having their respective leg members joined end-to-end in a butt joint to form said closed loop, the joined leg members of said U shaped laminations constituting the legs of said magnetic core, said core being formed by stacking alternate groupsof lon and short U-shaped laminations mating with corresponding groups of short'and long U-shaped laminations, the opposite legs of each of said U-shaped laminations being of unequallength but yet at the corresponding ends of the respective core legs in which they are positioned, joints for adjacent groups of laminations. lying in a given core leg being positioned at opposite ends of that core leg, joints for alternate groups of laminations lying in a given core leg being positioned at the same end of that core leg, and a staggered arrangement within each group so that joints for even-numbered layers within each group are progressively offset in the same direction and define a line running obliquely of the thickness of said layers of magnetic material, the joints for odd-numbered layers within each group being progressively ofiset in the same direction as joints of said evennumbered layers and also defining a line running obliquely of the thickness of said layers, the respective lines defined by the joints of said evenand odd-numbered layers within a given group being substantially parallel to each other but displaced from each other by a substantially greater distance than the distance separating any two adjacent joints lying on a given oblique line within that group, the two oblique lines defined by the joints of each group at an end of a given core leg being substantially co-linear with the two oblique lines defined by the joints of the other groups at said end of said core leg.

. FRANKLIN R. DENTREMONT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 509,770 Scott Nov. 28, 1893 1,935,426 Acly Nov. 14, 1933 2,380,300 Gaston July 10, 1945 2,393,038 Forbes Jan. 15, 1946 2,477,350 Somerville July 26, 1949 2,482,403 DEntremont Sept. 20, 1949 2,486,220 Somerville Oct. 25, 1949 

